It is standard practice in a machining operation, as for example disclosed in German Pat. No. 2,743,055, to filter magnetically attractable particles out of a liquid used for lubrication or cooling of a machining operation by passing the liquid through a treatment compartment in a vessel provided in this compartment with an array of spaced-apart magnetic bars, normally permanent magnets. As the liquid passes through the array between the bars the magnetically attractable particles--normally iron and steel fragments--stick to the magnets.
When these magnets become loaded with such particles it is standard practice to lift the array out of the vessel and scrape the adhering particles from the bars. Thus a free space above the machine must be provided which is large enough to accommodate the lifted-out bars. The scrapers also must be replaced frequently, as they are subjected to heavy abrasion by the normally very hard particles they are stripping off the bars. Thus such machines have substantial disadvantages.